In some conventional satellite communication systems, satellites or nodes orbit earth in a polar orbit. That is, the satellites orbit around earth in an orbit that crosses over the north and south poles. Although satellites in a polar orbit provide coverage over the entire earth, two problems exist.
First, polar-orbiting satellites create a counter-rotating seam. A counter-rotating seam is created by satellites travelling in opposite directions. For example, suppose satellites orbit from the south pole to the north pole. Once they pass the north pole, the satellites begin travelling in the opposite direction. Namely, the satellites then travel from the north pole to the south pole (i.e., the other half of the orbit). After passing the south pole, the satellites travel again in an upward direction toward the north pole. Thus, the counter-rotating seam is created by some satellites which are travelling on one-half of the orbit passing other satellites which are travelling on the other half of the orbit. The counter-rotating seam creates a problem of how to establish and maintain communication between satellites travelling in opposite directions.
Second, although polar-orbiting satellites optimize coverage for single satellite coverage for the entire earth, dual beam coverage may require doubling the number of satellites or adding more capability to the satellites themselves. However, doubling the number of satellites and adding more capability to a satellite significantly increases the cost of the system. Also, more weight is usually added to a satellite whenever the capability is increased.
Accordingly, it is an object of the present invention to provide a low-earth orbiting multiple satellite cellular communication system which eliminates a counter-rotating seam and provides continuous dual communication coverage over most of the earth.